斐波纳契数字在一定期限后变为负数 [英] Fibonacci numbers becoming negative after a certain term

问题描述

  program fibonacci $ b 
 
我在Fortran中编写了这个程序来显示斐波那契数列， $ b隐式无
整数:: x，p，c，i，t！初始化限制，上一个，当前，迭代和临时
 print *，列出第一个x斐波那契数字：
 read *，x！读取限制
p = 0！设置为零前
c = 1！将当前设置为1 
 do i = 1，x 
 print *，c ！打印当前的斐波纳契数字
t = c！将临时变量设置为当前的
c = c + p！将当前的当前值加上前一个
p = t！将之前的值设置为临时值
 end do！迭代直到达到限制'x'
结束程序fibonacci 
  

当我编译并运行它，并输入数字10时，它的确如预期的那样

 列出第一个x斐波那契数字：
 10 
 1 
 1 
 2 
 3 
 5 
 8 
 13 
 21 
 34 
 55 
  

但是当我输入50时：

 列出第一个x斐波纳契数字：
 50 
 1 
 1 
 2 
 3 
 5 
 8 
 13 
 21 
 34 
 55 
 89 
 144 
 233 
 377 
 610 
 987 
 1597 
 2584 
 4181 
 6765 
 10946 
 17711 
 28657 
 46368 
 75025 
 121393 
 196418 
 317811 
 514229 
 832040 
 1346269 
 2178309 
 3524578 
 5702887 
 9227465 
 14930352 
 24157817 
 39088169 
 63245986 
 102334155 
 165580141 
 267914296 
 433494437 
 701408733 
 1134903170 
 1836311903 
 -1323752223 
 512559680 
 -811192543 
 -298632863 
  

我不知道问题出在哪里，因为就我所见，这个逻辑很完美。我的错误在哪里？

我使用gfortran编译器。

显然你使用的是一个四字节的整数（ http://www-classes.usc.edu/engr/ce/108/text/ fbk01.htm ）。之后，1836311903你超过了最大整数值（2147483647），并且计算溢出了。

您有两种方法可以更精确地计算斐波纳契数。首先，您可以找到一个支持8或16字节整数的系统/ Fortran编译器组合。至少在gfortran支持，似乎由系统特定的。另一种选择是使用多精度库，例如 gmp 。

I wrote this program in Fortran to display the Fibonacci numbers up to the x-th term:

program fibonacci
implicit none
integer :: x,p,c,i,t !initializes limit, previous, current, iterative, and temp
print *, "List the first x fibonacci numbers: "
read *, x      !reads the limit
p=0            !sets previous to zero
c=1            !sets current to 1
do i=1,x
    print *, c !prints the current fibonacci number
t = c      !sets the temporary variable to the current
c = c + p  !sets the current to the current plus the previous
p = t      !sets the previous to the temporary value
end do         !iterates until it reaches the limit 'x'
end program fibonacci

When I compile and run it, and enter the number 10, it does as is expected

 List the first x fibonacci numbers: 
10
       1
       1
       2
       3
       5
       8
      13
      21
      34
      55

but when I entered 50:

 List the first x fibonacci numbers: 
50
       1
       1
       2
       3
       5
       8
      13
      21
      34
      55
      89
     144
     233
     377
     610
     987
    1597
    2584
    4181
    6765
   10946
   17711
   28657
   46368
   75025
  121393
  196418
  317811
  514229
  832040
 1346269
 2178309
 3524578
 5702887
 9227465
14930352
24157817
39088169
63245986
102334155
165580141
267914296
433494437
701408733
1134903170
1836311903
-1323752223
512559680
-811192543
-298632863

I don't know what the problem is, as far as I can see, the logic is sound. Where is my mistake?

I'm using the gfortran compiler.

解决方案

I'm no fortran expert, but I did take a class once...

Apparently you're using a four byte integer (http://www-classes.usc.edu/engr/ce/108/text/fbk01.htm) for these. After, 1836311903 you're exceeding the maximum integer value (2147483647) and the calculations are overflowing.

You have two options for calculating fibonacci numbers with more precision. First, you can find a system/fortran compiler combination that support 8 or 16 byte integers. Support in gfortran at least, seems to by system specific. Another option is to use a multiple precision library like gmp.

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